The present invention relates to mechanisms for obtaining a couple for maneuvering a component or part for rotating it on itself through a quarter turn, starting from a member which moves along a trajectory via a transmission.
As mechanisms of this type, notably for a large-diameter butterfly stopvalve actuator, the scotch-yoke, the crank-connecting rod support system, the rack and pinion and the wheel-tangent screw are already known. All these systems have the disadvantages of supplying an exaggeratedly large couple in certain operating phases and thus requiring oversizing of the control of the actuator to supply the couple required for maneuvering into every position.
French patent no. 1 460 561 expressly mentions that it relates to a mechanism driving a rotation shaft through a quarter turn with the transmitted couple increasing continuously from one end position to the other end position.
U.S. Pat. No. 5,000,072 proposes that a shaft 78 or 178 in FIG. 8 be driven by a lever arm 74 mounted on rollers 82. The patent is absolutely silent on the variation of the couple. It is clear, e.g. from FIG. 8, that there is a transition from one end position to the other by rotating through 90xc2x0 with a symmetry, with the result that the curve which has a maximum between 20 and 40xc2x0 according to the invention is not achieved.
Finally, U.S. Pat. 3,452,961 describes a device for controlling an actuator with variation of the couple, but it too proposes continuous variation of the couple, pointing out that in one end position a major couple and slow speed are required and in the other end position a small couple and high speed are required. The couple varies continuously without going through a maximum.
The invention overcomes the disadvantage of the prior art by means of a mechanism in which the transmission is such that the curve representing the coefficient of reduction, which is the ratio of the maneuvering couple to a nominal couple, shown on the y axis as a function of the angle of rotation, shown on the x axis, is convex with the upwardly facing convexity.
Thanks to this, the couple supplied can be adapted as a function of the couple required, thereby saving energy so that no oversizing is required. Preferably, the maximum coefficient of reduction is obtained with an angle of 20 to 40 degrees, more preferably between 28 to 37 degrees.
Among the various transmissions which give a curve is according to the invention, the particularly preferred one is the one in which the member moving along a trajectory is a slide on which is mounted, guided in a direction not parallel to the trajectory, a shoe securely attached to the component which is fixedly mounted but rotatable. The term xe2x80x9cshoexe2x80x9d in this specification also denotes a wheel or roller rolling along a rail and, generally speaking, any member moving along in the direction not parallel to the trajectory. This solution makes it possible to use any source of energy, be it manual, electrical, pneumatic, hydraulic or recoil energy stored in energy accumulating cartridges. The mechanism is irreversible for the manual and electrical solutions. The irreversibility of the other controls is ensured by the maintenance of pressure in the jacks. The arrangement is very simple and uses very few components.